Method of changing the frequency of single-phase induction-motors.



PATENTED JULY 7, 1903.

P. E. CHAPMAN. METHOD OF CHANGING THE FREQUENCY OF SINGLE PHASEINDUCTION MOTORS.

APPLICATION FILED APR. 15, 1902.

K0 IODBL.

NITED STAT S Patented July '7, 1903.

PATENT OFFICE.

METHOD OF CHANGING THE FREQUENCY OF SINGLE-PHASE INDUCTION-MOTORS.

SPECIFICATION forming part of Letters Patent No. 733,149, dated July '7,1903.

Application filed April 15, 1902.

To to whom it may concern.- 7

Be it known that I, PENROSE E. CHAPMAN, of the city of St. Louis, Stateof Missouri, have invented certain new and useful Improvements inChanging the Frequency of Single- Phase Induction-Motors, of which thefollowing is a full, clear, and exact description, reference being hadto the accompanying drawing, forming a part hereof.

My invention relates to changing the frequency of single-phaseinduction-motors.

My object is to render possible a reduction in frequency in smallinduction-motors, such as fan-motors, of, say, from sixteen thousandalternations to seven thousand two hundred alternations, whereby largenumbers of fanmotors of high frequency may be changed to lowerfrequency, and thereby be made more valuable. At the present time smallfanmotors of sixteen thousand alternations are worth little more thanjunk on the market, because of the universal change in frequency nowbeing made from a higher to a lower frequency by the electrical centralstations in the United States and other countries.

My invention consists of two or more phase or teaser coils, one placed,preferably, within the other, in combination with the main coils, eitherwound around one or several polar projections and connected in serieswith each other, said phase-coils being of higher resistance than themain coils and leading the latter in phase.

My invention consists, further, of the details of constructionhereinafter described and claimed.

The drawing is a diagrammatic view of a single-phase self-startinginduction-motor of the split-phase type.

1 indicates the usual bifurcated field polar projections, provided withthe slots 2 and carrying the main coils 3 and the latter connected inseries and provided with the usual circuit connections 4. and 5.

I am aware that the usual slotted types of fields used inalternating-current motors are interchangeable in frequency by simplyspacing the winding properly for the various frequencies, but am notaware that machines possessing poles similar to direct-current machineshave been or could be changed in fre- Serial No. 103,054. (No model.)

affecting the, shape of pole and general con-v struction, (althoughchanging the number of magnetic poles,) the principal difficultiesencountered being as follows: first, a too-great change in speed if thenumber of magnetic poles remain the same; second, inability to come upto speed when several polar projections are thrown together, forming onemagnetic pole, the motor having a decided tendency to run at a speedsomewhere between one-quarter and one-third full speed, depending onmethod of starting, load, &c., after having received its initial start,

My invention renders possible a change of frequency in machinespossessing polar projections similar to the usual D. G. pole indistinction to those possessing slotted or subdivided poles similar toslotted armatures and polyphase apparatus. The slots of the poles may ofcourse be of greater or less depth and located either centrally orotherwise relative to the poles. Heretofore when a machine of this typehas had two or more of its polar projections connected to form a singlepole, and thereby lower the frequency upon which the machine is adaptedto operate, or to increase the speed, and any of the usual startingdevices are used, the machine has been enabled to readily start; but ithas hung up in speed and refused to come up to its normal running speed.I overcome this difficulty by applying to the poles 1 two or more phaseor teaser coils 6 and 7, one within theother, in combination with themain coils 3 and either wound around one or several p0- lar projections,preferably as shown, and connected, preferably, in series with eachother,

said phase coils being of higher resistance and lower self-inductionthan the main coils, the currents in same consequently leading in phasethose in the main coils. The inner and generally the smaller phase-coil7 is preferably placed within the pole-slots 2 and extends from one hornor projection to a horn or projeotion of the next adjacent pole, thelarger phase-coil 6 completely encircling the same two poles which carrysaid smaller phase-coil and whereby said larger phase-coil will ofcourse inclose a greater polar surface.

8 indicates the armature-shaft, and 9 the usual armature used in thisclass of motors.

placement is mechanical, the angles referred to being thosecorresponding to the bipolar fields, as is usual in electrical-phasemeasurements.

What I claim is-- In induction-motors having poles similar todirect-current poles, bifurcated more or less by a single slotsubstantially as at present used in fan-motors of the split-phase type,the method of changing the frequency upon which the motor is adapted tooperate which consists in magnetizing several of the erstwhile polesmagnetically the same, and thereby reducing the number of magneticpoles, and combining therewith phaseor teaser coils of dififerent sizeone within the other, and

displaced in angular position about ninety degrees or a little less,substantially as specified. In testimony whereof I affix my signature inpresence of two witnesses.

PENROSE E. CHAPMAN.

Witnesses:

ALFRED A. EIoKs, JOHN C. HIGDON.

